The present invention relates to a device for the three-dimensional movement of a projected spatially light modulated beam, which can independently change the beam projection orientation in the azimuth and/or elevational direction without the projected modulated beam being rotated about its own optical axis if it is projected onto another location.
The projection devices of the present invention may be used for various illumination and lighting applications, in particular to obtain visual effects and for light pattern generation and as a gobo.
Typically, projectors project video or still images onto a fixed projection surface, so that the projections are bound to certain image positions. These projectors are fixed e.g. on a ceiling such that the projected light beam is fixed with respect to the projection surface.
In show, advertising and simulation applications, in stage and theatre lighting, however, a three-dimensional movement of the projection beam is often desired.
Furthermore, in lighting, a spotlight may for example be placed on a person or on a detail in a scene. In order to obtain special effects, this spotlight is often focussed on a gobo, a small circular aperture with a pattern on it. Typically, multiple different gobo shapes (patterns) are obtained by placing the gobos into a cassette or the like which is rotated to select between the different gobos. The gobos themselves can also be rotated within the cassette.
Previously, gobos were passive devices. A digital gobo is described in U.S. Pat. No. 5,828,485. In a digital gobo, a light valve is used, which can change the pattern on the gobo on demand.
One application of stage lighting is projection of an image for shadowless lighting, or provision of a shadowless follow spot, which is lighting of a person where no shadow falls behind that person. This is done by determining the shape of the performer on stage, e.g. by infrared detection, and by identifying its borders. Those borders are used to define an outline that is slightly smaller than that of the performer. That outline is supplied to dynamically variable gobo for modulation of the projected light. As the performer continues to move, the changing border shape is followed and a new outline is defined which is fed to the means for producing a new outline spot, used as a new gobo for the light. In order to be able to follow the performer on stage, the projector must be able project the images in all directions.
One way to achieve the goal of projecting images all around, is putting a projector on a movable mount. For a high performance a heavy projector would be required and this would call for a substantial mount and powerful motors. It is preferred to use light-weight devices and to reduce the power consumption and operating noise level and to increase reaction speed, such as the speed of direction changes. Cable connections should be flexible and light in weight to reduce loads on stage support frames. Furthermore, such a moving device is not advisable for bright xenon lamps inside the projector, as the light-emitting arc can become unstable when subjected to rapid accelerations.
WO 98/18037 describes a method and device for the three-dimensional movement of the projection beam of a video or graphics projector. The projection beam, coming from a light source and guided over and/or through an opto-electronic image generator and through a projection lens, is deflected by means of at least one mirror to be swivelled about two axes, an X-axis extending in direction of incidence of the projection beam and a transversely extending Y-axis. The projector is thus fixed, only the mirror rotates. It is the diverging image beam coming out of the projection lens which is deflected. The rotation of the mirror generates a rotation of the projected image, which is compensated for by means of an additional rotation of the image carrier (e.g. the DMD mirrors) in a forced coupling with the swivel movement of the mirror. The construction of the device is rather complex.
U.S. Pat. No. 4,235,535 describes a projection apparatus for projecting images on a cylindrical screen for purposes of simulating the view from a ship and being included in a ship simulator. Light coming from an image producing device is sent through a duct towards a projection lens, a stationary mirror and a movable mirror. In the duct, a derotation prism such as a dove prism is provided to make sure that the image as projected in different directions is always upright. Such a derotation prism adds to the complexity of the beam deflection assembly and furthermore reduces image quality.
In U.S. Pat. No. 4,702,699 is described a target image representation system, used e.g. in a target acquisition training system. An image carrying beam coming from a projector is sent into an image deflection assembly comprising a support column and an image deflection head rotatable on the column about the vertical axis of the column. A first reflecting element redirects the image carrying beam into a vertical path along the axis of the column. A second reflecting element fixedly mounted in the deflection head then redirects it back into a horizontal path. A third reflecting element which is rotatably mounted in the deflection head for rotation about the axis of the image carrying beam directed thereto, redirects it again into a path at right angles to the horizontal path. The beam reflected from this third reflecting element passes through a window and projects the image on the screen. Rotation of the deflection head about the vertical axis of the column causes a change in the azimuth of the projected image, while the rotation of the reflecting element about the horizontal beam axis causes a change in the elevation of the image on the screen. Rotations of the reflecting elements in producing the desired azimuth and elevation of the target image give rise to rotations of the target image about the beam axis. This is solved according to U.S. Pat. No. 4,702,699 by including in the projection means an image generating means for generating target images which are to be projected by the beam and which are oriented to compensate for image rotation by the image beam deflection assembly.
There is also known from WO 94/08425 a light projecting apparatus for projection of visual information onto viewing surfaces. An optical system attached to the final output of a projector varies orientation relative to the projector on either single or multiple viewing surfaces. A tiltable and rotatable mirror is provided for moving the image, as well as an image rotator assembly in order to pre-rotate the image so that it is always projected upright. The image rotator assembly adds to the complexity of the system.
It is an object of the present invention to provide an improved projection system for three-dimensional movement of a projected spatially modulated light beam where the light generating projection lamp is not subject to high accelerations and therefore does not become unstable.
It is a further object of the present invention to provide an improved projection system for three-dimensional movement of a projected spatially modulated light beam where the projected beam is not rotated about the beam axis when projecting the beam towards different locations.
The above objectives may each be accomplished by a projection system for three-dimensional movement of a projected spatially modulated light beam comprising: a light source, a spatial light modulation unit for projecting a spatially modulated light beam and an optical path from the light source to the spatial light modulation unit. The spatial light modulation unit may include a spatial light modulator and a projection lens. The spatial light modulator may be a light shaping device, especially a digital light shaping device or an image forming device, especially a digital image forming device. The spatial light modulator generates a spatially modulated light beam, either monochromatic, e.g. white, or coloured, when light falls in on it from a non-image modulated light beam from the light source. The spatial light modulator is moved with the projection lens as a combined unit by a driving mechanism. As the spatial modulated light beam is generated at such a location that the spatially modulated light beam is not deflected anymore before arriving at the projection lens, there is no rotation of the shaped light or image beam around the axis of the beam, whatever the direction of projection, i.e. independent of the direction of projection. The spatial light modulator may be any suitable modulator such as a light valve, a transmission LCD light valve, a reflection LCD light valve, a DMD or similar.
The present invention also includes a method of projecting a spatially modulated light beam which is non-rotating with respect to its own optical axis when the beam is projected in differing directions, comprising the steps of:
a) generating a spatially unmodulated light beam from a light source;
b) projecting the light beam towards a spatial light modulation unit along a light path;
c) forming a spatially modulated beam from the light beam using the spatial light modulator unit;
d) projecting the modulated beam; and
e) moving the projected beam through space by rotating the spatial light modulator unit with respect to the light source. The method may comprise rotating the spatial light modulation unit about two orthogonal axes of rotation. Each axis of rotation may locally coincide with an optical axis of the light path.
These and other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.